Process of producing pure zinc oxid.



s'rarrns PATENT, OFFICE.

HENRY WILLIAM or. STUGKL'E, OF PARISFRANCE.

PROCESS OF PRODUCING PURE ZINC OXID.

Specification of Letters Patent.

Patented-nonun on.

Llltiudtiat Ito Drawing. Application filed February 18, 1814. Serial No. 819,355.

To all whom it may concern:

, 'Bc iii-known that I, Hnunr WILLIAM on S'ruckcn', 'a citizen of'the United States of (Americziyrcsidiug at Paris, France, have invented certain new and useful Improve ments in Processes of Producing Pure Zinc Oxid, of which the following is a specification. 1

This process relates to the manufacture of pure zinc oxid or pure metallic zinc, using zinc minerals, more particularly those mincr sis, the proportion of zinc in which is too low to be treated by metallurgical processes, 01: any salt of zinc as a raw material. I .41 The present invention consists in lnnvmtzinc from the minerals 1n the wellknown manner b means of a suitable acid, such as sulfuric, ydrochloric, or nitric acid. The acid used is preferably mixed with sufiicient quantity of water in order to aVOld 2O crystallization of the zinc salt durin lixiviation. Thesolutions obtained are eprived,

in the usual manner of foreign metals which are also artly dissolved by the acid. From 5 the pur' ed solutions zinc is precipitated in the form of zinc sulfite by a solu ion of ammonia sulfite. After the filtration and washing, the zinc sulfitc is calcined. The residue of calcining is pure oxid of zinc which is suitable for all known urposcs, that is to say, as a white pigment or painting and also as raw material for the manufacture of pure metallic zinc. The sulfur dioxid which escapes during the calcining, is used for regenerating the ammonia sulfite. According to a known process, sulfite of zinc is prepared by causing a solution of an alkali sulfite to act on an equivalent quantity of a dissolved salt of zinc. Under these conditions, a portion of the zinc used is however not precipitated and remains dissolved in the mother lye. This circumstance is not an obstacle in the manufacture of sulfite of zinc in a laboratory, but in the manufacture $5 ofthis product on a large scale, it is a great obstacl: as the quantity of zinc which escapes precipitation, reduces the yield by 10-20%. In the process according to this invention, these losses are avoided, and practicall' the whole of the zinc is precipitated, caustib ammonia or carbonate of ammonia being added to the reaction mixture or to the ammonia sulfite used for the same, during or before the reaction. This action of arm monia could not have been expected, since 11; as is known, most zinc precipitates are, on

' reaction with the ammonia sulfite, produces acid sulfur dioxid.

the contrary dissolved by an excess of canstic ammonia or carbonate of ammoniav ;The caustic ammonia or the carbonate ofIammonia can also be produced during or before the reaction by adding to the reaction, mixture or to the ammonia sulfite used for w the same, an alkali, such as h drate'of lime or carbonate of sodium,whic by a double.

ammonia or carbonate of ammonia.

. The sulfur dioxid produced during calpining of zinc sulfite, is utilized for producmg ammonia sulfite, so that the latter is alu ays regenerated, as already stated. v According to a known process, ammonia sulfit'e is produced by sulfur vdioxid being" absorbed in ammonia water. This process} would not be suitable for the present inventtion, as sulfur dioxid which escapes during the calcining of zinc sulfite or of zinc blend, contalns a certain quantity of air, and it has been found that: 1. during the absorption of sulfur dioxid in ammonia Water in the, presence of air, a large portion of the ammonia sulfite formed, is oxidized to ammonia sulfate, which results in a considerable loss of sulfur dioxid; 2. the air added, in passing throu h the ammonia water carries r 1 1 away a consi crablc quantity of ammonia, 35 which results in a loss of ammonia. It has). been further found that ammonia sulfite ox idizes' considerably less in the presence of a 3' free acid than in the presence of a free alkali, and that the losses just referred to, can be avoided by absorbing sulfur dioxid not in caustic ammonia, but in a solution of' I neutral or slightly acid ammonia sulfite. If) For that purpose, a slightly alkaline ammo nia sulfitc could also be used, as a sli ht al- 95 kalinity is quickly rendered harmless y the As at the ordinary temperature ammonia sulfite, as well as ammonia bisulfite in water solution, is not volatile, no ammonia. can be carried away by the current of air, and moreover the ammonia-sulfite at once becomes acid owing to the sulfur-dioxid absorbed, so thatthe oxidation to sulfate in these conditions is only slight, as already stated. The sulfur dioxid dissolvedin ammonia sulfitc as a bisulfite, is subsequently neutralized with caustic ammonia, outside the absorbing apparatus, namely in a closed tank, in order to;avoid carnation by the air. 110 The mom" required for the 'purpose is obtained from the ammonia salt produced\ during the precipitation of zinc sulfite by double reaction, in accordance With the following equation:

Z11SO4+ ouigaso znso mngeso Vfhat it claim is:

1 A cyclical process of producing pure zinc oxid, which consists in reacting upon a dissolved zinc salt- With ammonium sulfite in presence of caustic ammonia or ammonium carbonate, calcining the precipitated zinc sulfite and utilizing the evolved sulfur dioxid. for regenerating the ammonium sulfite.

2. A cyclical process of producing pure zinc oxid, Which consists in reacting upon a dissolved zinc salt with ammonium sulfite in presence of caustic ammonia or ammonium carbonate, calcining the precipitated zinc sulfite, introducing the evolved sulfur'dioxid into a solution of ammonium sulfite, thereby producing ammonium bisulfite, and converting said ammonium bisulfite into n1on0-sulfite for use in a repetition of the cycle.

In testimony "whereof I affix my signature in presence of two Witnesses.

uanai' Wittnn n1 s'raciita Witnesses:

Lucien Duonnenn, Hanson U. Conn. 

